This invention relates to a thermoplastic resin film having a good gas barrier property and to a method of producing same. The present invention is also directed to a cushioning material using the above film.
One known thermoplastic resin film having a gas barrier property is a composite film having a core, gas barrier layer formed of a polyamide, two adhesive layers provided on both sides of the core layer, and two surface layers formed of a polyolefin and provided for covering the adhesive layers. Such a composite film, however, is difficult to prepare and requires a complicated extrusion machine. Additionally, there is not available a fully suitable adhesive for bonding the surface layers to the core layer.
A gas barrier film is also known which includes a matrix film formed of a polyolefin and containing fine particulate resin having a gas barrier property and uniformly dispersed in the matrix. While such a blend film may be fabricated more easily as compared with the above composite film, the gas barrier property of the blend film is not so excellent as the composite film, unless the particulate resin is used in a large amount. Further, the blend film lacks clarity because of the light scattering caused by the very fine particulate resin contained in the film.
U.S. Pat. No. 3,950,476 discloses a synthetic film containing at least two unmixed polymeric components, which film is characterized in that at least one of the components occurs in the form of substantially endless or continuous threads in the longitudinal direction of the film. The threads have transverse dimensions that are at least a few times, for instance at least two to five times, smaller than the thickness of the film, and the threads are embedded in a basic mass of a different polymeric component. Because of the presence of the threads, this film has a high strength and is suitable to be used for packing of heavy weight granular materials such as cement. This United States patent is silent with respect to gas permeability of the film. Because the embedded components are in the form of threads, the film has poor gas barrier properties.